We have shown that long-term cultures of renal glomeruli are capable of producing erythropoietin in significant quantities. The objectives are to further develop the culture system, including establishing human glomerular cultures, in order to provide a source of hormone for research and clinical testing. Basic mechanisms regulating erythropoietin production and release will be studied in hormone- producing cultures exposed to hypoxic and steroidal stimuli by seeking the underlying enzymatic determinants and correlates of altered hormone production. Purification and chemical characterization of culture- produced hormone will be approached by use of affinity chromatography. Efforts will also be made to isolate erythropoietin-sensitive and erythropoietin-producing cells by application of this method. Mechanisms underlying erythropoietin effects on erythroid stem cells will be studied by inducing selective survival and stimulation of erythropoietic committed stem cells in spleen colonies of irradiated mice. Repeated dosages of Fe 55 which are "suicidal" to iron incorporating red cell precursors by virtue of internal radiation will be used to produce this isolated population of stem cells. Effects of erythropoietin on this cell population will be studied histologically and biochemically.